Move Comes as Providers Battle for U.S. Market Share and Seek to Trim Subsidies

U.S. wireless carriers have rejiggered the prices of their service plans again, extending a period of unusual volatility triggered by an aggressive push for customers by T-Mobile US Inc.

AT&T Inc. is cutting prices on its wireless plans for the second time this year, lowering the monthly cost of a plan offering unlimited calls and texts and two gigabytes of Internet use by $15. The new plan, which begins Sunday, would lower the...